This invention relates to a webbing length adjustor, and in particular to adjustors which use clamping elements that have cam shaped surfaces to clamp webbing with respect to the adjustor.
Such adjustors are commonly used with restraint and seat belt webbing. The webbing which passes through the adjustor has tension applied on one side of the adjustor which locks the webbing with respect to the adjustor. Pulling the webbing on the other side of the adjustor will release the clamping force and allow the webbing to be pulled through the adjustor.
For example, a shoulder harness in a child restraint or safety seat uses such an adjustor to allow tensioning of the shoulder straps. A locking cam in the adjustor is shaped so that applying tension to the free end of the webbing will cause rotation of the arm to release the webbing. The webbing can then be pulled through the adjustor to tighten the shoulder straps.
After adjusting the webbing, the cam is caused to rotate to a locking position to apply clamping force to the webbing.
The rotation of the cam is assisted by a spring which moves the cam in the required direction to clamp the webbing. The surface of the cam has a series of ridges which bite into the webbing surface. The cam is shaped so that further tension applied to the webbing causes it to rotate further and to thereby increase the clamping force.
Known adjustors have a manual actuator which enables rotation of the cam to release the clamping force and allow the webbing to move in either direction through the adjustor. This enables loosening of the webbing when increased length is required for a seat belt or shoulder harness. A spring is required to ensure that the cam rotates far enough to enable the serrated edges of the cam to abut against the webbing. This engagement will then ensure that the clamping force applied to the webbing will increase as the tension applied to the webbing increases.
The aim of this invention is to provide an alternative arrangement of adjustor and to have an adjustor which has a reduced number of components with an improved ease of manufacture and assembly.
The invention is therefore said to reside in a webbing length adjustor adapted to clamp webbing having a free end and a tension end when tension is applied to the tension end of the webbing, the adjustor comprising;
a webbing guide,
a clamp element pivotally mounted with respect to said webbing guide,
a locking cam on said clamp element which in a locked position clamps said webbing between said locking cam and said webbing guide to prevent movement of said webbing through said adjustor when said tension is applied to the tension end,
a release actuator to cause rotation of said clamp element to move said locking cam to a position where said webbing is released to allow it to move in either direction through said adjustor, and
a projection on said clamp element that abuts against the webbing between the locking cam and the tension end thereof so that said webbing when tensioned exerts a force against said projection which urges or causes rotation of said clamp element in a direction that holds or moves said locking cam in or into said locked position.
As can be seen from the above description, the invention avoids the need for the use of a spring to rotate the locking element into a position where it engages the webbing. Instead, the projection causes a deflection of the webbing when the clamp element rotates to an unlocked position. Tension applied to the webbing acts to straighten the deflected webbing. This causes a force to be applied to the projection which rotates the clamp element and locking cam towards the webbing.
The projection can be designed to always slightly deflect the webbing, even when the clamp element is in its locked position. This will ensure that there is some positive force urging the locking cam towards the webbing. Rotation of the clamp element by application of tension onto the webbing will cause further gripping of the locking cam against webbing. The greater the deflection of the webbing, the more force is applied to the projection when tension is re-applied to the webbing.
The webbing guide may comprise a bracket which has a surface over which the webbing locates. The locking cam acts to clamp the webbing against the surface. In a case of child restraints, the bracket may be adapted to be attached to the molded shell of the restraint.
Alternatively, where the webbing length adjuster is associated with a child safety seat, the shell of the child safety seat may be molded to form the required webbing guide. The clamp element can then be pivotally attached with respect to the molded webbing guide.
Preferably, the locking cam has a surface designed to grip or otherwise positively catch against the surface of the webbing. This surface may have knurling or a plurality of saw tooth projections that extend the width of the locking cam surface. Each saw tooth projection has a sharp edge which will dig into and grip the surface of the webbing.
The release actuator preferably comprises a manual actuator. This may be a flange which is lifted or pushed by a person""s fingers. By lifting or pushing the flange, the clamping element may be rotated to release the webbing.
Alternatively, the release actuator comprises a button actuator which may be used to cause rotation of the clamp element.
The projection on the clamp element may be of an arcuate flange that extends away from the axis of rotation of the clamp element.
The webbing guide may be provided with a recess into which the projection locates. The webbing is pushed into the recess by the projection so that its path from the locking cam is into the recess, around the end of the projection and back out of the recess and onto a surface of the webbing guide. This can result in a more positive force being applied by the webbing to the projection when tension is applied to the webbing.
Alternatively, the invention may include any form of projection that deflects the line of the webbing so that a rotation force is applied to the cam element when tension is applied to the webbing.